In life science chemistry, for example, there are a wide number of applications that involve preparation, storage and analysis of a large number of samples. Such applications include drug discovery, including combinatorial chemistry, and Polymerase Chain Reaction (PCR) experiments. In these applications reaction tubes, vials or the like are often filled or part filled with reagents and the tubes sealed prior to further processing. In addition, multi-well plates, consisting of an array of tubes, are now used extensively in molecular biology laboratories and elsewhere.
A number of ways for sealing such tubes have been developed over the years. For example, a foil or plastic film may be applied across the entire upper surface of a plate of tubes. Thus heat sealable aluminium foils or adhesive plastic films are commercially available. Once applied, these films provide an efficient, gas and liquid-tight seal but are tiresome to apply and remove. Access to each well can only be obtained by piercing the film or by peeling off the film by hand or with a foil stripper. Consequently, this type of seal is not reusable, and is not suitable for robotic application or removal. Furthermore, the seal does not reform automatically if a sample is withdrawn with a syringe needle, pipette tip or cannula for example.
Alternatively, a seal may be achieved by placing a relatively heavy, flexible rubber mat over the entire surface of the plate. The weight of the mat and any plate(s) stacked on top of the mat keep the seal in place. It is important that the mat does not slide over the top of the plate in order to avoid cross-contamination. In the case of 96 well plates, this is achieved by having 96 raised dimples or “pimples” an the surface of the mat in an array that matches exactly the array of wells. Each dimple is sized and shaped to sit firmly into a well. Once in place, no lateral movement of the mat is possible because the perimeter of each dimple fits snugly within its respective well. However, such mats do not produce a complete, fluid-tight seal and some evaporation can still take place.
If a more fluid-tight seal is required then a cap can be applied to each tube. Strips of caps are available for multi-well plate, examples of which are sold by Advanced Biotechnologies Limited under Catalogue No AB0784. Such caps can include a piercable or septum region usually in the centre of the cap, which is easily piercable with a needle. This allows material to be withdrawn from or added to the tube or well without, supposedly, damaging the cap. However, each time a needle is inserted through the cap it causes some damage to the septum region as it punctures the surface. A syringe needle, however small, tends to act like a cutter, removing a fragment of cap each time it penetrates. Eventually, after a number of such penetrations, the damaged area no longer forms a fluid-tight seal.
Sealing devices for sealing tubes are also known from WO 83/01912 (Labsystems OY) which incorporate a slit or a channel designed to allow the passage of a pipette or capillary tube. The slits in these sealing devices are formed from two straightsided components that mate together. To be effective, the channel must remain tightly closed at all times, even when a pipette is inserted through it. However, when the pipette is withdrawn the sealing device must not have a tendency to withdraw from the tube along with the pipette. These two requirements tend to be mutually incompatible. On the one hand, a firm, liquid-tight seal is required when the sealing device is in place and the channel is unpenetrated. This requires that the opposing walls of the channel must be forced very firmly against each other. These same forces also tend to grip any pipette, needle or capillary tube that is introduced into the channel very firmly. This firm grip on the pipette etc. tends to cause the sealing device to work its way up and out of the tube as the pipette is withdrawn. This problem is compounded if multiple samples (multi-sipping) are required.
It is an object of the present invention to overcome or at least mitigate some or all of the problems outlined above.